1. Field of the Invention:
The present invention is generally related to a switch which is actuated in response to a change in its attitude or tilt and, more particularly, to a tilt switch which utilizes a conductive sphere which pivots about one of two support edges between two positions in which one position completes an electrical circuit by bridging the gap between the two support edges and another position breaks the electrical circuit by moving out of contact relation with one of the two support edges.
2. Description of the Prior Art:
Many different types of tilt switches are known to those skilled in the art. Some tilt switches are intended to detect very slight changes in the attitude of the switch and respond to small changes in the angle of tilt. For example, the well known Mercury switch is used in both residential and commercial thermostats and can detect changes in attitude as small as one or two degrees. Other types of tilt switches are intended to discern much larger changes in the angle of tilt. For example, certain vehicles can be provided with tilt switches which break an electrical circuit and deprive motive power to a vehicle when that vehicle leans beyond an acceptable angle. This type of tilt switch can be used as a safety precaution on vehicles, such as bulldozers or tractors, which can be made to operate on steeply sloped terrain. Although a wide variety of switches of these types are very well known to those skilled in the art, only a select few will be discussed herein.
U.S. Pat. No. 4,628,160, which issued to Canevari on Dec. 9, 1986, discloses an electrical tilt switch that comprises a generally cylindrical cap member that has a hollow interior with an internal inwardly extending ridge that is positioned a significant distance above its lower edge. It also comprises a generally cylindrical base member that has a concave upper face. An annular insulating member is interposed between the base and the cap and the three components are fastened together. Inside this assembly, a spherical contact member is carried on the dished surface of the base and is moveable by rolling against the ridge when the switch is tilted beyond a predetermined angle.
U.S. Pat. No. 4,833,281, which issued to Maples on May 23, 1989, describes a motion detector that is adapted for use with the transmitter of a motor vehicle keyless entry system. It causes the transmitter device carried by the user to transmit a coded signal when it is in motion, for example, as it is being carried by a user toward the vehicle. The motion detector includes a spool disposed within and electrically insulated from a shell. A ball is positioned in the annular cavity around the spool. An electronic circuit is provided to sense a change in state of the motion detector as an indication of motion. These changes of state of the motor detector occur when the ball moves into and out of direct contact with the spool or shell and further as the ball rolls around the annular cavity while being supported by both the spool and shell caused by surface roughness of the interior surfaces.
U.S. Pat. No. 4,297,683, which issued to Roberts on Oct. 27, 1981, describes a vandal alarm system for parking meters to prevent the unauthorized entry into the coin box area of a parking meter and to prevent the striking of the housing as well as the bending of the support pipe. A radio transmitter is adapted to send signals to a receiver which is constantly turned on. The received signal indicates unauthorized entry or vandalism to parking meter and to the particular parking meter from which the signal is sent. Switches are actuated at an opening of the timer compartment and/or coin box area. A switch is also actuated while the supporting post is bent. A timer is placed in this circuit so that only after a determined time period is a signal sent of the bending of the post.
U.S. Pat. No. 4,135,067, which issued to Bitko on Jan. 16, 1979, discloses a tilt switch that includes an enclosure for a gravity response conductive ball. An annular shelf surrounds a central depression where at least one switch contact passing into the housing is exposed. The shelf is operable to support the ball in a position resting against a cup-shaped portion of the switch housing with the ball centroid located within an imaginary right cylinder having the inner shell periphery as a base. In response to the tilting of the switch, the ball is movable away from the cup-shaped housing to the depression where it engages the contact and closes a circuit between that and another contact.
U.S. Pat. No. 4,618,746, which issued to Schwob et al on Oct. 21, 1986, describes a ball actuated position sensitive switch that is multi-directional. It comprises a housing in which at least two electrical contacts are arranged opposite to one another. A tilting member is supported in the housing by means of a tilting part and has a control part extending in the vicinity of one of the electrical contacts. A ball is carried by a surface of the tilting member that is opposite the tilting part. The tilting member has a profile in the form of a cup.
U.S. Pat. No. 4,467,154, which issued to Hill on Aug. 21, 1984, describes a gravity switch that comprises a molded cup-shaped dielectric member and a cup-shaped conductor member which are pressed together to comprise a integral dimensionally stable sealed enclosure for a contact member that is moveable axially therein for selectively making or breaking an electrical connection between the cup-shaped conductor member and a second conductor extending axially through and sealed with the base of the cup-shaped dielectric member. The outer surfaces of the base and the second conductor comprise electrical contacts for a gravity actuated switch. The overall axial dimension between the axially outer surfaces is obtained by telescoping the cup-shaped members coaxially together until the preselected axially dimension is obtained.
U.S. Pat. No. 4,686,335, which issued to Grant on Aug. 11, 1987, discloses a shock sensor switch that is vibration sensitive and comprises a pair of spaced apart parallel contacts housed in a switch body and a movably supported activated mass inside a chamber in the body. The mass is supported by conductive members in the form of a pair of bars secured in the mass and located between the two contacts with the center of gravity of the mass spaced from the points of contact between the contacts and the bars so that bars are urged against the contacts by a lever action as a result of the gravitational force acting on the mass. The forces at the contact points are thus greater than that which would be obtained by simply allowing the mass to rest on the contacts, which enables a relatively small mass to be used having a greater sensitivity to high frequency vibrations.
Many problems exist with regard to the manufacture and use of the tilt switches which are presently known to those skilled in the art. For example, certain applications require that electrical currents flow through a spherical conductor which is moveable and one or more stationary conductors. To accomplish this function, tilt switches generally require that the spherical conductor roll along a predefined path to move from a conductive position to a nonconductive position, and back again. However, when electrical current is made or broken by the spherical conductor moving into contact or out of contact with a stationary conductor, it is common for arcing to occur. This arcing can create pitting on the surface of the sphere. The pitting can then interfere with the smooth rolling of the conductive sphere during later cycles of its operation. Another problem with existing tilt switches is the cost of manufacture and assembly which is often prohibitive in applications that require inexpensive switches to permit the application to be economically justifiable.
It would therefore be advantageous for a tilt switch to be easily and inexpensively manufacturable while avoiding the need for a spherical member to roll along another surface within the switch.